The mobile phone provider said 1,827 accounts were accessed, potentially providing criminals with customers’ names, mobile numbers, bank sort codes and the last four digits of their bank accounts. But no credit or debit card details were accessed and the information obtained by the criminals “cannot be used directly to access customers’ bank accounts”.

A Vodafone spokesman said: “This incident was driven by criminals using email addresses and passwords acquired from an unknown source external to Vodafone. Vodafone’s systems were not compromised or breached in any way.” It has also emerged that online comments by a Talk Talk representative may have unwittingly encouraged hackers to test the telecom firm’s cyber defences in the run up to the latest hacking attack. One of the firm’s customer service representatives wrote on Twitter that information about some of Talk Talk’s customers held by Carphone Warehouse data systems may not have been encrypted. However, this information does leave these 1,827 customers open to fraud and might also leave them open to phishing attempts.” Vodafone is the second British telecoms company being hit with a hack attack.

Talk Talk has now confirmed that as many as 1.2 million email addresses, names and phone numbers were exposed, along with 21,000 bank account numbers and sort codes – information which could be used by criminals attempting to scam customers. It is thought these potential weaknesses may have been the subject of discussion on online forums used by hackers in the weeks before the most recent attack took place.